This invention relates generally to automatic assembly machines for picking up and placing component parts in an assembly process. More particularly, the invention relates to such automatic machines used in the fabrication of micro-electronic or hybrid circuitry requiring the accurate placement of integrated-circuit or discrete-component chips onto a substrate.
In the fabrication of hybrid circuitry, there is a requirement for extremely accurate placement of a plurality of chips on a substrate, prior to bonding of the terminals or leads of each chip to appropriately connect it with other components on the substrate. A chip may be placed directly on the substrate, or it may be held in place by solder paste applied to selected faces or edges of the chip, or by an epoxy adhesive which may serve as an electrical connection, a heat sink, or both. The chips are generally of various sizes, from a few hundredths of an inch to a few tenths of an inch square, and they must be positioned on the substrate at various positions to an accuracy of a few thousandths of an inch. Fabrication of a single chip-substrate assembly includes the steps of picking up a plurality of chips of different sizes, applying solder paste or epoxy to the chips as required, and accurately positioning the chips, each at its designated position on the substrate. This positioning accuracy has to be precisely repeatable at a rapid rate, so that relatively high production capacities may be reached.
Chip placement machines of the prior art generally operate on an "assembly line" principle, wherein a substrate is indexed, on some type of conveyor, through a succession of work stations at which the chips are accurately positioned by appropriate feeding and positioning means. Before being operated at production speeds, such a machine has to be carefully "set up" so that the chip positioning means at each work station places a chip at exactly its desired position on the substrate.
Chip placement machines of the foregoing general type are satisfactory for long production runs on a particular chip-substrate assembly, but the need for careful and painstaking set-up of the machine prior to each production run makes it less satisfactory for medium and short production runs.
Two other manufacturing or machine-tool techniques which might be applied to the chip assembly process are numerical control, and manipulation by programmable machines, sometimes referred to as robots. The numerical control technique is normally "externally" programmed, i.e., the movements of a tool or work-piece are preprogrammed and encoded on paper tape, magnetic tape, or some other medium external to the machine. However, differences between theoretical and actual displacements can result in substantial positional errors, and numerical control has not been successfully adapted to the chip assembly process.
In programmable manipulators, or robots, desired movements of a tool or work-piece are programmed by "walking" the machine through the movements and recording the various parameters or co-ordinates of the movements in an internal storage or memory. The movements can be, in effect, "played back" repeatably any number of times, thereby performing the programmed functions at a much higher speed than could be attained by a human operator, This type of manipulator has been used extensively in automobile manufacture, particularly for spot welding of car bodies. Such manipulators used for spot welding generally control the movement of a pair of welding electrodes on a pivoted and extendable arm. The accuracies required for spot welding operations are, of course, much less demanding than those required for chip assembly processes, and no known chip assembly machine available heretofore operates on the programmable manipulator principle.
Although the programmable manipulator has inherent advantages, such as absolute repeatability and ease of programming, its application to the chip assembly process is made difficult by the stringent requirements of that process. Basically, these requirements are three-fold. First, the capability of movement of the chips to the substrate must be such that a satisfactorily high production rate is obtained. Second, the positioning of the chips must be highly accurate, preferably to within 0.002 inch. Finally, the machine must be capable of picking up very small components of variable size, processing them at an intermediate station, and transferring them to desired positions on the substrate.
It will be appreciated from the foregoing that there is a real need in the hybrid circuitry fabrication art for a chip assembly machine which utilizes the principles of programmable manipulators, which may be easily operated by relatively unskilled operators, and which, therefore, may be efficiently utilized for medium and short production runs, as well as long production runs. The present invention satisfies this need.